Pressure pour apparatus



Oct. 17, 1967 w. E. WILLIS PRESSURE POUR APPARATUS 2 Sheets-Sheet 1 Filed Nov. 30, 1965 R m M M P Y mw m T R E NT E N E 5 L V E S P N 0 0 m a T MA N I D EL 5 R R RN F A M W8 United States Patent 3,347,427 PRESSURE POUR APPARATUS Wilfred Ernest Willis, San Francisco, Calif., assignor to James S. Campbell, doing business as Quality Casting Systems Filed Nov. 30, 1965, Ser. No. 524,955 14 Claims. (Cl. 222-399) ABSTRACT OF THE DISCLOSURE In a pressure pour apparatus, discrete pour and ready to pour pressures are permitted because such pressures are controlled from a point below the level of material to be poured, by locating pressure sensing means at the desired point below the liquid level and controlling the pour and ready to pour pressures from this point.

My invention relates to apparatus for pressure pouring of liquid from a receptacle, and more particularly to the pressure pouring of molten metal from a receptacle such as a furnace or crucible.

Basically, the employment of a pressure medium such as gas under pressure, to bring about pouring of molten metal from a receptacle such as a furnace or crucible, is old, but insofar as is known, the gas employed for this purpose, is conducted directly into the space above the liquid level to create a gas cushion, the resulting build up of pressure thus directly developed in the region above the molten metal, then causing a discharge of metal through a discharge or pouring tube, with a corresponding lowering of liquid level in the receptacle.

Not only is the pouring rate under these conditions, a function of the changing liquid level, but, unless care is exercised, any lowering of the level of the molten metal below the level at which the metal enters the pouring tube, will result in loss of gas and gas cushion, thus necessitating a complete build up of gas pressure following refilling of the receptacle in preparation for subsequent pourings.

Also, and of probably greater significance is the hazard of spraying molten metal from the nozzle due to the velocity of the gas as it rushes through the pouring tube.

Among the objects of my invention are:

(1) To provide novel and improved pressure pour apparatus for dispensing of liquid;

(2) To provide novel and improvedpressure pour apparatus of the type employing gas under pressure as a propellant;

(3) To provide novel and improved pressure pour apparatus of the type employing gas under pressure as a propellant, and wherein lowering of liquid level below the level at which liquid enters the pouring tube is automatically precluded;

(4) To provide novel and improved pressure pour apparatus of the type employing gas under pressure as a propellant, wherein a substantially constant rate of discharge may be realized, irrespective of changing liquid level in the receptacle from which the liquid is dis pensed;

(5) To provide a novel and improved pressure pour apparatus of the type employing gas under pressure as a propellant, wherein a constant flow rate of discharge may be maintained with gas supplied to the receptacle at a constant pressure, regardless of change in liquid level in such receptacle;

(6) To provide novel and improved pressure pour apparatus of the type employing gas under pressure as a propellant, wherein the difference in pressure of such gas between the ready to pour state of such apparatus and the pour state may be minimized to the point of rendering the change from the one condition to the other quite fast;

(7) To provide novel and improved pressure pour apparatus which lends itself to refilling the receptacle from which liquid is dispensed, without adversely affecting operating pressures;

(8) To provide novel and improved pressure pour apparatus of the above type, adapted primarily for the dispensing of molten metal from a receptacle such as a furnace or crucible;

(9) To provide novel and improved pressure pour apparatus of the above type for molten metal, adapted for repeat dispensing of substantially equal quantities of such molten metal;

(10) To provide novel and improved pressure pour apparatus ideally suitable for the dispensing of nonferrous metals in molten condition from a receptacle such as a furnace or crucible;

(11) To provide novel and improved pressure pour apparatus of the above type for the dispensing of molten metal, wherein such metal in its molten state will be cleansed and thoroughly protected against contamination at all times from furnace or crucible to a mold in which such metal may be poured. Additional objects of my invention will be brought out in the following description of a preferred embodiment of the same, taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a view depicting the invention in schematic form; and

FIGURE 2 is a circuit diagram applicable to the invention.

Referring to the drawings for details of my invention in its preferred form, the apparatus may involve a scalable receptacle 1 which may take the form of a crucible or furnace, such receptacle including a cover or roof 5, provided with a fill opening 7, capable of being sealed by a closure 9.

Extending out of such receptacle from a level 13 adjacent the interior bottom of the receptacle is a discharge passageway in the form, preferably, of a pouring tube 15 terminating in a pouring lip 17 above the maximum level of liquid 18 contemplated within the receptacle. Preferably, such pouring tube extends upwardly through the cover or roof of the receptacle, and includes a bend 19 at a point above the receptacle to bring the pouring lip to a location convenient for handling of liquid being poured therefrom.

The pouring tube may be heated to assure maintenance of flow therethrough and under proper temperature conditions, and all components of the apparatus being described as holding or carrying molten metal, may be insulated against heat loss.

Affixed to the upper end of the pouring: tube, is a downwardly directed nozzle assembly 21, such nozzle assembly forming a significantly acute angle with the pouring tube at the lip junction therewith.

Means is provided for conducting a gas under pressure into' the receptacle, such means preferably taking the form of a gas inlet tube 23 entering the receptacle, preferably through the roof thereof, and terminating at a level 24 substantially below the maximum contemplated level of molten metal in such receptacle, but above the lower end of the dischargepassageway or pouring tube. This relationship as will be seen, is vital to the present invention. e

In prior apparatus employing gas under pressure to effect pouring, and where the gas is supplied directly 'to the space above the molten metal, a fixed pouring rate can not be readily maintained, due to the lowering of, the liquid level in the receptacle as the liquid is dispensed 3 therefrom. The ability to maintain a uniform flow rate becomes of considerable importance where repeat pouring of quantities of metal of uniform weight is the goal to be realized. 7

Considering only the sealed receptacle 1, the pouring tube 15, and the inlet tube 23 for conducting gas into the sealed receptacle below liquid level, and disregarding for the moment, everything else such as the piping associated with these components, and related electrical circuitry, discharge of molten metal from the nozzle occurs when the molten metal in the pouring tube rises above the lip. Preferably, and for practical purposes, pouring should be accomplished with the liquid level at some point 27 above the lip, to assure full capacity flow, such level being designated the pour level.

During non-pouring periods, liquid level in the pouring tube must be at some point below the lip, which point may be designated the ready to pour level.

During transition from the pour level to the ready to pour level, cut-off of flow will occur when the liquid level drops below the lip level of the pouring tube.

These three levels become quite significant in the operation involved in the present invention, and the apparatus for achieving the same.

Assuming an arbitrary ready to pour level in the pouring tube at some such point 29 below the lip, and considering the level 24 at the lower end of the gas inlet tube as determining a horizontal reference level, then the pressure within the receptacle must be sufiicient to support a column of molten metal of a height 33 equal to the distance from the horizontal reference level 24 to the ready to pour level 29.

Such pressure, it will be noted, is not a function of the gas cushion pressure alone, but a function of the combination of this pressure and the prevailing depth 35 of the molten metal to the horizontal reference level 24. Thus the gas entering the receptacle from the outside, must be at a pressure equal to this combination pressure, in view of the fact that it emerges from the inlet tube at the horizontal reference level, below the liquid level in the receptacle, and is not introduced directly into the region above the liquid level, and this becomes significant.

To increase the height of this column from the ready to pour to the pour level 27, will accordingly necessitate a corresponding increase in pressure of the gas supplied to the receptacle. As pouring proceeds under these conditions and the liquid level in the receptacle correspondingly lowers, the pressure contributed by the molten metal in the receptacle toward sustaining the height of molten metal in the pouring tube will therefore diminish, and to sustain the molten metal at the pour level, will necessitate a corresponding increase in the pressure of the gas cushion. This, in the apparatus as thus far described, automatically adjusts itself so long as the incoming gas is maintained at a fixed pressure value.

Being that it is a relatively simple matter to maintain pressure of a gas constant, it follows that a very precise control can, therefore, be maintained in the pouring characteristics at the discharge end of the apparatus.

As the liquid level drops and the gas cushion pressure automatically increases, as previously indicated, then when the liquid level reaches the horizontal reference level 24, which, it will be recalled, coincides with the lower end of the gas inlet tube 23, the gas cushion pressure will have reached the pressure value of the incoming gas, and thus at this point, will still sustain a column of liquid reaching to the pour level.

However, any further lowering of the liquid level in the receptacle, will in effect, lower the reference level, and while the gas cushion pressure will be sufficient to sustain a column of molten metal of the same height, the column as a whole will begin to drop with lowering of the liquid level in the receptacle below the lower end of the gas inlet tube.

By making the distance between the lower end of the gas inlet tube (horizontal reference level 24) and the lower end of the discharge passageway (level 13), greater than the distance between the pour level 27 and the lip 17, it will be appreciated that the upper end of the column will reach the level of the lip before the level of the liquid in the receptacle can reach the lower end of the discharge passageway. This relationship is very important to the present invention, in that, should an operator permit the liquid level to drop below the horizontal reference level 24, discharge at the nozzle will automatically cease before the lower end of the discharge passageway can be exposed to permit escape of gas and loss of the gas cushion.

The afore-mentioned relationship between the gas inlet tube and the discharge passageway lends itself with great advantage, to use with a receptacle having a sloping bottom 39, with the discharge passageway 15 terminating at its lower end in the deepest portion of the receptacle and the gas inlet tube 23 terminating at a higher point therein. With such an arrangement, the useful capacity of the receptacle is substantially increased, and the receptacle can be practically emptied without loss of gas cushion pressure.

From the foregoing discussion of the invention as thus far described, it is only necessary to supply to the receptacle, gas at either of only two pressures, despite the fact that the gas cushion pressure will fluctuate with change in liquid level. One such pressure is the pour pressure, which once established, becomes somewhat critical in value, while the other pressure is that required to hold the apparatus in a ready to pour status, with the column of liquid at the ready to pour level.- This latter pressure, it will be appreciated, is not so critical, though the apparatus becomes more sensitive in its operation as the ready to pour pressure which is selected, brings the column closer to the level of the lip, it being noted that the closer this level is to the level of the lip, the more sensitive will be the apparatus to a change in pressure necessary to effect pouring. Thus the apparatus lends itself to adjustment such that the difference betweenthe pour pressure and the ready to pour pressure may be rather small, thus making it possible to effect a quick response of the apparatus from the ready to pour state to the pour condition.

In providing for such selective pressures of gas to be supplied to the receptacle, a source 41 of gas under pressure, exceeding in value the pour pressure desired, is connected to the gas inlet tube 23 through a regulator 43 and a gas pressure regulator 45, adjusted to the ready to pour pressure. In a branch flow circuit around the ready to pour regulator, is a pressure regulator 47, adjusted to the pour pressure. A valve 49 in the pour pressure branch, permits selective application of the pour pressure when desired, and for automatic or semi-automatic operation, this valve will preferably be one of the solenoid operated type in which case, a solenoid winding 51 will be associated therewith.

An adjustable needle valve 53 in the flow path to the gas inlet tube 23 may be employed to adjust flow of gas to the receptacle.

Transient pulsations of gas flow from the supply source 41 to the receptacle 1 may be minimized by the coupling of a reservoir or accumulator 55 to the flow line leading to the ready to pour and the pour regulators.

With the pour regulator branch line blocked by the valve 49, gas can flow to the receptacle only at the ready to pour pressure, which as previously indicated, is adjusted to maintain the column at the ready to pour level 29, just below the lip of the pouring tube.

By opening the valve in the pour regulator branch line, the pressure of gas flowing to the receptacle will promptly jump to the pour pressure and increase the column height to the pour level.

Upon restoration of the ready to pour pressure, the column height will drop back to the ready to pour level,

but it is significant to note, however, that in so doing, pouring ceases-when the column drops to the lip level, and does not have to await the full period of change from the pour level to the ready to pour level before pouring ceases.

Apparatus, as thus far described, lends itself admirably to the pressure pouring of molten metal and enables expansion of such apparatus to encompass features of particular merit, when such apparatus is employed in the pouring of metal in its molten condition.

In handling non-ferrous metals, for example, such as aluminum, magnesium, and the like, and their alloys, remarkably improved characteristics of such metal may be realized when such metal, in its molten state, is cleansed and protected against contamination, and this may be readily .accomplished, and in a very simple manner, through utilization, as the pressure gas, an inert gas such as dry nitrogen or argon, whereby the gas flowing from the lower end of the gas inlet tube 23, will percolate up through the molten metal to remove hydrogen inclusions and other impurities in the metal at the time; and the pressure cushion formed above the metal, will serve to maintain the molten metal under a blanket of the inert gas at all times, thus protecting it against oxidation and contamination from atmospheric and other sources.

. Of interest in this connection, also, is the fact that the gas in percolating upward through the molten metal will expand rapidly due to the intense heat of the molten metal with which it is in direct contact, and such rapid expansion of the gas brings about much quicker build up of pressure in the gas cushion than otherwise.

A porous closure 56 at the discharge end of the gas inlet tube will break up the gas to form smaller bubbles and thus eifect a more efficient cleansing actionas the gas percolates up into the gas cushion chamber above.

a To extend the protection by the inert gas to other points where such protection might be desirable, I provide a flow line 57 from the gas cushion to the point in the apparatus where the nozzle assembly connects with the pourin tube, whereby the upper end of the column of molten metal will also be blanketed under inert gas, and thus likewise isolated from atmospheric and other sources of possible contamination. A'needle valve 59 in this flow line may be adjusted to control flow therein, which flow at best, will be more in the nature of a leak.

.With such flow line installed, elevation of the column ofmolten metal from the ready to pour level to the fpour level will build up pressure in the region adjacent the end of the pouring tube, and such pressure, if permited free increase, might conceivably interfere with ability of the column to reach the desired pour level. It therefore becomes desirable to provide some relief from possible excessive build up of pressure at this point.

I, accordingly, couple into this flow line, at a high point adjacent the discharge end of the pouring tube, a

pressure switch 61 adjusted to respond to a rise in pressure at this point, to a value deemed insulficient to adversely affect the ability of the column of molten metal to reach the pour level, and cause this pressure switch to bring about a partial venting of the gas flowing from the gas cushion to this region.

Specifically this may be accomplished by providing a vent line 63 from the flow line 57, and installing in this vent line, a normally closed solenoid valve 65 having a solenoid winding 67 to be controlled through the pressure switch. I

Inasmuch as this solenoid valve will open during pouring, the inert gas escaping through the vent line might, to great advantage, be directed to escape around the nozzle assembly, so as to blanket with the inert gas, a mold during the pouring of such mold.

The quantity of molten metal discharged during any pour, is a function of discharge flow rate and time, and inasmuch, as previously indicated, the flow rate can be readily maintained constant by accurate control of the pressure of gas supplied to the receptacle, the accuracy of the quantity discharged then becomes a factor of accuracy of timing.

Toward this end, the pressure switch, which functions at the start of a pour cycle, is utilized to control a timing circuit or mechanism which restores the pour valve to its closed condition at the end of a predetermined period of pour.

During a pour cycle, it will be appreciated that the pressure of the gas cushion will exceed that necessary to support the column of molten metal at its ready to pour level, and consequently, at the termination of a pour cycle, the rapidity with which the column drops from the pour level to the ready to pour level, is a function of the rate at which the gas cushion pressure may be reduced to a value, which, in combination with the then existing height of liquid in the receptacle above the horizontal reference level, will sustain a column at its ready to pour level. A rapid return to the ready to pour pressure, under the circumstances is obviously to be desired.

I have been able to attain this goal, and at the same time, take advantage of the situation to achieve a sharp cut-01f or termination of a pour cycle. This I have accomplished by installing a gas fiow line 69 in shunt with or around the needle valve 59 located in the leak flow line to the upper end of the discharge passageway or pouring tube, and in this shunt line, I include a pressure regulator 71 acting as a relief valve and a normally open solenoid valve 73 controlled by a solenoid winding 75.

The relief valve is adjusted to open at a pressure just slightly above the pressure to which the ready to pour regulator 45 is adjusted, but below the pour pressure, and its control end is gas coupled to the downstream side of the ready to pour regulator, where it would also be exposed to the higher pressure from the pour regulator during a pour cycle.

When thus connected, the relief valve 71 in the shunt circuit around the needle valve will open when exposed to control pressures exceeding the ready to pour value, a condition which exists during a pour, when it will be exposed to pour pressure at the.pour regulator 47.

With the relief valve 71 thus open, and if, at the end of a pour cycle, the solenoid valve 73 were opened, a blast of inert gas from the receptacle 1 will strike the molten metal at the end of the pouring tube and split the molten metal at the lip, driving the column down the pouring tube toward the ready to pour level, and the outside portion through the nozzle assembly. In this connection, the acute angle of surfaces at the lip is effective in assuring a sharp cut-off.

In this connection, it is important to note that this blast, originating as it does, at the gas cushion, will serve to rapidly drop the gas cushion pressure toward the ready to pour value, which is just the performance desired at this point in the operation of the apparatus.

With the same set-up, the relief valve 71 is capable of protecting the apparatus against faulty operation in the event the ready to pour regulator should malfunction during a quiet period and permit a rise in pressure sutficient to cause opening of the relief valve 71. The valve 73 being in open condition between pour cycles, gas will be released from the gas cushion. Accidental discharge of molten metal from the receptacle is thus precluded.

Inasmuch as the gas cushion pressure increases with lowering of the liquid level, it therefore may be relied on as an indication of the liquid level in the receptacle. A pressure gauge in the flow line 57, suitably calibrated in terms of liquid level with thus conveniently furnish this information, in addition to actual prevailing gas cushion pressure.

An electrical circuit capable of functionally relating the various valves and timing means referred to, is illustrated in FIGURE 2 of the drawings to which reference will now be made. i

Across the lines 81, 83 of a power source 85, is a series arrangement of a spring biased start switch 87, and a spring biased stop switch 89, the normally closed contacts 91 of a timing mechanism 93, and the holding coil 95 of a relay 96 having a pair of normally open contacts 97 connected in shunt across the start switch. Upon pressing the start switch, the relay will become energized and close its contacts around the start switch to effect a holding circuit.

In parallel with the relay coil 95 are the solenoid winding 51 of the normally closed solenoid valve 49 located in the branch line of the pour regulator 47, and the solenoid winding 75 of the normally open solenoid valve 73 located in the shunt line of the relief valve 71. Thus, upon closing the start switch 87, the gas flow line to the pour regulator 47 will be opened and the shunt line 69 around the needle valve 59 will be blocked.

When the metal flows over the lip into the nozzle assembly, it will block free flow of gas through the leak flow line 57.

The resultant prompt build up of pressure adjacent the discharge end of the pouring tube will immediately urge the pressure switch 61 to its closed condition, such switch being connected from one side of the stop switch 89 through the winding 101 of a relay 103 having normally open contacts 105 shunting the pressure switch, whereby upon energization of this relay, its contacts will close to establish a holding circuit.

In parallel with this relay winding is the solenoid winding 67 of the normally closed solenoid valve 65 located in the vent line 63, and accordingly this solenoid valve unblocks such line when the solenoid winding of this valve is energized.

Thus all conditions will have been established for initiating a pour.

The duration of pour may be controlled manually, by merely pressing the stop switch 89 when desired, which in turn de-energizes the holding relay winding 95, the winding 51 of the solenoid valve associated with the pour regulator, and the winding 75 of the solenoid valve associated with the relief valve '71, as a result of all of which, the relay contacts 97 will open to break the holding circuit, the flow line through the pour regulator 47 will be blocked, and the shunt line 69 around the needle valve 59 will be unblocked at the valve 73.

The opening of the stop switch 89 will at the same time, remove power from the relay winding 101, and the winding 67 of the solenoid valve 65 in the vent line, with the result that the relay contacts 105 shunting the pressure switch will open to break the holding circuit, and the solenoid valve 65 in the vent line will close. Thus all conditions will have been re-established for the ready to pour status of the apparatus.

While the pour cycle can thus be determined manually, autmoatic control of the pour cycle can be realized by the inclusion in the circuit, of the timing mechanism 93, which in this instance, controls the normally closed contacts 91 previously mentioned. The timing means is connected through a manually controlled switch 111, in parallel with the winding 101 of the holding relay 103 and the winding 67 of the solenoid valve 65 in the venting line. With the timing mechanism connected in circuit, it will, after a pre-set period of operation, momentarily open the normally closed contacts 91 associated therewith, which will have the same effect as the manual opening of the stop switch as previously described.

Thus all conditions satisfying the requirements for the ready to pour status of the apparatus will automatically be restored upon completion of the predetermined time period for the pour cycle as established by the timing means.

To initiate a subsequent pour cycle will again require manual closing of the start switch.

From the foregoing description of my invention in its preferred form, it will be apparent that the same fulfills all the objects attributed thereto, and while I have illustrated and described the same in its preferred form, it will be apparent that the same is subject to alteration and modification without departing from the underlying principles involved, and I accordingly do not desire to be limited in my protection to the specific details illustrated and described except as may be necessitated by the appended claims.

I claim:

1. Pressure pour apparatus for dispensing of liquid comprising:

a scalable receptacle for holding liquid,

a discharge passageway extending upwardly from said receptacle, with its lower end at a level adjacent the bottom of said receptacle and having at its upper end, a discharge lip,

means for conducting a gas under pressure into said receptacle,

and pressure sensitive means exposed to pressure prevailing in said liquid at a location below the prevailing liquid level and responsive to diminution thereof from a value corresponding to the pressure value of said pressure sensitive means for admitting gas under pressure to maintain pressure at said below level point substantially equal to the pressure value of said pressure sensitive means.

2. Pressure pour apparatus in accordance with claim 1, characterized by means for feeding gas into said receptacle via said gas conducting means, and at a pressure suflicient to support a column of such liquid in said discharge passageway at a ready to pour level therein, below said discharge lip.

3. Pressure pour apparatus in accordance with claim 2, characterized by means for increasing said gas feed pressure to a value sufficient to increase said column to a pour level, above said discharge lip.

4. Pressure pour apparatus in accordance with claim 3, characterized by said means for feeding gas into said receptacle at ready to pour pressure, including a source of gas under pressure exceeding pour pressure, a flow line connecting said source to said gas conducting means, and said pressure sensitive means including a pressure regulator in said flow line and adjusted to said ready to pour pressure.

5. Pressure pour apparatus in accordance with claim 4, characterized by said means for increasing said gas feed pressure, including a branch line about said ready to pour pressure regulator, a regulator in said branch line adjusted to said pour pressure and included in said pressure sensitive means, and a valve in said branch line, adapted in one position, to block gas flow in said branch line, and in another position, to permit gas flow.

6. Pressure pour apparatus in accordance with claim 1, characterized by means for feeding gas under pressure into said receptacle via said gas conducting means and sufficiently to support a column of such liquid in said discharge passageway at a ready to pour level therein, below said discharge lip. i

7. Pressure pour apparatus in accordance with claim 3, characterized by said gas conducting means terminating below liquid level in said receptacle with the distance between the lower end of said gas conducting means and the lower end of said discharge passageway being greater than ihe distance between said pour level and said discharge 8. Pressure pour apparatus in accordance with claim 3, characterized by a nozzle assembly affixed to the lip end of said discharge passageway.

9. Pressure pour apparatus in accordance with claim 8, characterized by a leak flow connection from the region in said receptacle above ful-l liquid level to the region above pour level adjacent the discharge end of said discharge passageway.

10. Pressure pour apparatus in accordance with claim 9, characterized by use of an inert gas.

11. Pressure pour apparatus in accordance with claim 6, characterized by means for efliecting a sharp cut-01f of flow at the lip at the termination of a pour cycle.

12. Pressure pour apparatus for dispensing of liquid comprising;

a sealable receptable for holding liquid,

a discharge passageway extending upwardly from said receptacle, with its lower end at a level approaching the bottom of said receptacle and having at its upper end a discharge lip,

means for conducting a gas under pressure into said receptacle, said means terminating at a level substantially below tfull liquid level, but above the lower end of said discharge passageway,

a nozzle assembly afiixed to the lip end of said discharge passageway,

and sharp cut off means for directing a blast of gas into the region above said lip to effect a splitting of a flowing molten metal at said lip.

References Cited UNITED STATES PATENTS 2,086,000 7/1937 Roren 222-399 X 2,182,742 12/1939 Brewer 222-399 3,229,337 1/ 1966 Holz et a1 22-79 ROBERT B. REEVES, Primray Examiner. STANLEY H. TOLLBERG, Examiner. 

1. PRESSURE POUR APPARATUS FOR DISPENSING OF LIQUID COMPRISING: A SEALIBLE RECEPTACLE FOR HOLDING LIQUID, A DISCHARGE PASSAGEWAY EXTENDING UPWARDLY FROM SAID RECEPTACLE, WITH ITS LOWER END AT A LEVEL ADJACENT THE BOTTOM OF SAID RECEPTACLE AND HAVING AT ITS UPPER END, A DISCHARGE LIP, MEANS FOR CONDUCTING A GAS UNDER PRESSURE INTO SAID RECEPTACLE, AND PRESSURE SENSITIVE MEANS EXPOSED TO PRESSURE PREVAILING IN SAID LIQUID AT A LOCATION BELOW THE PREVAILING LIQUID LEVEL AND RESPONSIVE TO DIMINUTION THEREOF FROM A VALVE CORRESPONDING TO THE PRESSURE VALUE OF SAID PRESSURE SENSITIVE MEANS FOR ADMITTING GAS UNDER PRESSURE TO MAINTAIN PRESSURE AT SAID BELOW LEVEL POINT SUBSTANTIALLY EQUAL TO THE PRESSURE VALUE OF SAID PRESSURE SENSITIVE MEANS. 